The present invention relates to an arrangement for controlling flow of fluid to a component of a gas turbine engine.
Components in a gas turbine engine are subject to elevated temperatures, often above the melting point of the material or materials from which they are formed. Hence there is a need for cooling of these components, which is conventionally provided by film or impingement cooling of the hot components using relatively cool air ducted from one or more compressor stages. The extraction of air from the compressor stages reduces the amount of air available as working fluid to be supplied to the combustor and turbines of the gas turbine engine. Typically 5 to 10% of the compressed air at an intermediate pressure compressor stage may be extracted to provide cooling to turbine rotor blades and turbine stator guide vanes of one or more turbine stages.
Such cooling systems must be rated for the highest temperature condition in the engine cycle, usually at take-off and maximum climb. However, at other times in the engine cycle, particularly at cruise, less cooling is required. Therefore, it is desirable to modulate the amount of air extracted during these periods to the minimum required to provide adequate cooling. Thus, more air remains as working fluid in the gas turbine engine and hence more output power is achieved.
One known method of modulating the flow of cooling fluid, depending on the engine cycle condition, is detailed in EP 1,632,649 and comprises a magnetic valve located in the cooling air supply conduit. The magnetic valve has at least one member that comprises a ferromagnetic material. The valve has a first configuration in which the valve at least partially restricts the supply conduit and a second configuration in which the supply conduit is substantially unrestricted. The configuration of the valve is dependent on the temperature of the ferromagnetic material.
In one embodiment of this prior art, in an inline magnetic valve 10, as shown in FIG. 1, the ferromagnetic material 14 is a block located within an enlarged portion of a supply conduit 12 and in thermal contact, therefore, with the flow of a cooling fluid shown by arrow 16. A permanent magnet 18, or an electromagnet, surrounds the enlarged portion of the supply conduit 12 so that, when the ferromagnetic material 14 is below its Curie temperature, the ferromagnetic material block 14 at least partially restricts the flow of cooling fluid 16. When the temperature of the fluid, and therefore of the ferromagnetic material block 14, increases towards the Curie temperature of the block 14, the block 14 loses its magnetism and is pushed along the conduit 12 by fluid pressure or another mechanism. Stops 20 may be provided to support the block 14 such that the fluid flow 16 is substantially unrestricted through the conduit 12.
One problem with this method of modulating the cooling fluid flow is that the magnets required to resist the fluid flow are large. This means that they have a large thermal inertia and, therefore, the response time of the valve is relatively long; typically in the order of a few seconds. In some applications, particularly within gas turbine engines, this is unacceptably long.
Another problem with this method of modulating the cooling fluid flow is that the valve components are bulky and heavy. In some applications, particularly within the core of a gas turbine engine, there is little space to accommodate additional components and weight is critical.